Alpha-synuclein (?-Syn) is one of the most abundant proteins in the CNS that is known to be a major player in the neurodegeneration observed in Parkinson?s disease. We show that stroke (transient focal ischemia) upregulates ?-Syn protein expression and nuclear translocation in neurons of adult rodents and humans. We further show that knockdown or knockout of ?-Syn significantly decreases the infarction and promotes better neurological recovery in rodents subjected to focal ischemia. Based on these exciting new leads, in this proposal we wish to test the therapeutic potential of targeting ?-Syn in post-stroke brain by following the criteria set by the Stroke Treatment Academic Industry Roundtable (STAIR) consortium. Aim 1 is to evaluate the window of therapeutic opportunity, effect of sex, age, route of administration and toxicity of ?-Syn siRNA therapy following focal ischemia in rodents. We further observed that a microRNA called miR-7a potently targets ?-Syn. Importantly miR-7a showed an inverse relation to ?-Syn (miR-7a levels were down-regulated while ?-Syn levels were upregulated after stroke). Hence, we will test the efficacy of replenishing miR-7a in the post-stroke brain to repress ?-Syn and thus decrease brain damage. Testing alternate approaches to target a protein gives better opportunities for future clinical translation. Hence, miR-7a mimic therapy will serve as an alternate approach to ?-Syn siRNA therapy. Aim 2 is to evaluate the window of therapeutic opportunity, effect of sex, age, route of administration, toxicity and long-term effects of miR-7a mimic after focal ischemia. The mechanisms that contribute to ?-Syn-mediated secondary brain damage after stroke are not well understood. We demonstrate that ?-Syn protein formed in excess in brain during the acute phase after stroke oligomerizes and forms aggregates with time. We further show that ?-Syn promotes brain damage by multiple pathologic mechanisms including mitochondrial fission. In chronic neurodegeneration, ?-Syn is known to act as an essential scaffolding molecule for the activation of GSK-3? and the subsequent Tau hyperphosphorylation that leads to activation of Drp1 which promotes mitochondrial fission. In preliminary studies we observed increased phosphorylation of GSK-3?, Tau and Drp1. In Aim 3, we will test if ?-Syn promotes post-ischemic mitochondrial fission and brain damage by involving GSK-3? and Tau. The long-term goal of these studies is to evaluate if targeting ?-Syn is a viable option for stroke therapy in both males and females and at different ages.